lock

This function places an advisory lock on a shared variable or referenced
object contained in THING until the lock goes out of scope.

The value returned is the scalar itself, if the argument is a scalar, or a
reference, if the argument is a hash, array or subroutine.

lock() is a "weak keyword" : this means that if you've defined a function
by this name (before any calls to it), that function will be called
instead. If you are not under usethreads::shared
this does nothing.
See threads::shared.

perldoc.perl.org - Official documentation for the Perl programming language